The ability to add branch pipes to existing main gas or water pipelines has long been required. The safest method is to isolate the section of main pipeline, depressurize, purge, cut a hole, clean out, and permanently attach a tee adapter and short section of branch pipe. However, in order to minimize service interruptions to nearby gas/water customers, hot tapping tools have been developed which can cut into the main pipeline while still in service, under gas or water pressure. This prior art involved attaching a branch saddle tee and short branch pipe section prior to cutting a hole in the main pipeline. A temporary clamp was placed around the main pipeline for support and hot tapping fixture was attached to the clamp. The tapping fixture included a compression seal butted against the end of the short pipe branch, a drill mounted on a shaft extending through the compression fitting and means to advance/retract the drill and compression seal. After the hole was drilled, the drill bit was retracted towards the compression seal within the now pressurized branch pipe. If a fullflow valve was not included in the branch pipe, a squeeze off tool was then used to seal the lower portion of the pressurized branch pipe, prior to removal of the temporary clamp around the main pipeline and the tapping fixture. After attaching the remainder of the branch pipe to the tapped section, the full flow valve is opened or the squeezed section rerounded. Other hot tapping tools required permanent branch pipe valves and fittings for attaching and sealing.
Several problems are inherent to these prior art techniques. The temporary main pipeline clamp installation/removal requires extensive excavation/backfilling for buried pipelines. Restricted access may prevent installation of the temporary pipeline clamp in some locations.
A second problem is that the cut hole segment is not positively retrieved. Although the main pipeline pressure tends to blow the cut segment out, the cutter tends to push it into the pipeline. If mainline flow or gravity overcomes the pressure tending to blow out cut segment, segment can damage downstream equipment.
A third problem is that the branch pipe must be separately tested for leakage prior to cutting into mainpipe or risking dangerous leakage after cutting the hole segment. If separate testing is accomplished, additional equipment is required. Additional time for set up is needed, resulting in higher cost.
A fourth problem is that upon removal of the tool, a portion of the pressurized branch pipe is discharged to the immediate area. In the case of water, this could be a high pressure stream capable of injuring people. In the case of gas, an explosive or flammable mixing could occur in the confines of an underground excavation, leading to potential disaster.
The type of tapping tool adapted to a single size of pipe or which required fittings for attachment offered little flexibility. Different tools or adapter sections were required. Leak testing of just the branch pipe was also not possible since it was not isolated. For larger sizes, the mating fittings added weight and stress to the pipe joint. Alignment of the permanent branch fittings was also required.